Issue of this bug is that most part of fftw is not thread safe, only compute-intensive fftw_execute & co are. Since smoke was affected by this issue as well, a global fftw mutex was added to BLI_threads. Audaspace also uses fftw in one of its readers (AUD_BandPassReader.cpp), but this is not an issue currently since this code is disabled in CMake/scons files. There was another threading issue with smoke, we need to copy dm used by emit_from_derivedmesh(), as it is modified by this func. Reviewers: sergey, brecht Reviewed By: brecht CC: brecht Differential Revision: https://developer.blender.org/D374